How to copy array of C strings to C++ std::vector<std::string>?

Question

The accepted answers in

populate the vector at the same time as declaring it:

vector<string> vec(cArray, cArray + cArrayLength)

But what if I need to do it separately because I need to expand the scope of the vector, e.g. in

vector<string> vec;
if (some_condition)
    // copy a char** to vec
else
    // copy another char** to vec
do_something(vec);

How do I copy the arrays then?

vec.assign(cArray, cArray + cArrayLength);

Kerrek SB
– Kerrek SB

2016-01-15 16:12:52 +00:00
Commented Jan 15, 2016 at 16:12 — Kerrek SB
– Kerrek SB, Commented Jan 15, 2016 at 16:12
std::copy and std::back_inserter too..... research!!

Lightness Races in Orbit
– Lightness Races in Orbit

2016-01-15 16:22:50 +00:00
Commented Jan 15, 2016 at 16:22 — Lightness Races in Orbit
– Lightness Races in Orbit, Commented Jan 15, 2016 at 16:22

Violet Giraffe · Accepted Answer · 2016-01-15 16:14:45Z

2

std::vector provides an assignment operator:

std::vector<std::string> vec;
if (some_condition)
    // copy a char** to vec
    vec = std::vector<std::string> vec(cArray, cArray + cArrayLength);
else
    // copy another char** to vec
    vec = std::vector<std::string> vec(cArray, anotherCArray + anotherCArrayLength )

answered Jan 15, 2016 at 16:14

Violet Giraffe

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Comments

Harish krupo · Accepted Answer · 2016-01-15 16:16:15Z

1

You can always use the copy constructor as

if(cond)
{
    vec = std::vector<std::string>(std::begin(arr1), std::end(arr1));
}
else
{
    vec = std::vector<std::string>(std::begin(arr2), std::end(arr2));
}

answered Jan 15, 2016 at 16:16

Harish krupo

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Comments

Jerry Coffin · Accepted Answer · 2016-01-15 16:20:50Z

1

A couple of answers have already pointed to creating a temporary object, then assigning the result to your destination. As long as you're using C++11 (or later) where this will be done as a move assignment, that's generally quite acceptable.

Another possibility that will work well with older compilers (and new ones) would be something like:

char **src;
size_t len;

if (cond) { 
    src = cArray;
    len = cArrayLen;
}
else {
    src = CAnotherArray;
    len = CAnotherArrayLen;
}

vector<string> vec(src, src+len);

answered Jan 15, 2016 at 16:20

Jerry Coffin

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